Apparatus for indicating an open electrical circuit



Nov. 24, 1964 G. MARGULIES 3,158,713

APPARATUS FOR INDICATING AN OPEN ELECTRICAL CIRCUIT Original Filed Sept.27, 1960 I I? I4 I53 u l6 INVENTOR. GERALD MARGULIES ATTORNEYS UnitedStates Patent 3,158,713 APPARATUS FOR INDICATING AN OPEN ELECTRICALCIRCUIT Gerald Margulies, 9130 Bradford Road, Silver Spring, Md.

Continuation of application Ser. No. 58,861, Sept. 27, 1966). Thisapplication May 22, 1963, Ser. No. 285,187 1 Claim. (Cl. 20087) (Grantedunder Title 35, US. Code (1952), sec. 266) The invention describedherein may be manufactured and used by or for the Government of theUnited States of America for governmental purposes without the paymentof any royalties thereon or therefor.

This application is a continuation of my copending application Ser. No.58,861, filed September 27, 1960, for Electromagnetically ControlledIndicator and now abandoned.

The invention relates to improvements in indicating the condition ofprotectors or fuses for electric circuits and more particularly to suchimprovements utilizing an indicator which is operative at all times toshow the condition of such protectors.

As is well known, protectors for electric circuits are of numerous typesand employ a fusible element which is enclosed in a suitable housingsuch as, for example, a cylinder of insulating material for preventingthe component parts of the protectors from damage or deterioration.Additionally, the protector housings are constructed of various sizesand shapes to be readily received in or removed from receptaclesprovided in the circuits with which the protectors are to be used.

When numerous circuits are provided in an installation, such as thoserequired on shipboard, it is practically impossible for maintenancepersonnel to make the necessary tests of a number of protectors for theelectric circuits before the particular protector that has acted to opena circuit can be located. This is too time-consuming and is more or lessof a hit-or-miss proposition.

Various attempts have been made in trhe past to develop protectors forelectric circuits which have indicators associated therewith in order toeliminate the necessity of manual inspection of the protectors. Some ofthese have been arranged to give an audible indication that a circuithas opened while others have provided for a visual indication of such acondition. One prior and commonly used indicating arrangement forvisually showing that a protector or fuse has blown and that a circuitis open has been to arrange an incandescent lamp and series resistor inthe circuit, across the fuse, in such a manner that when the fusedcircuit was operating properly, the lamp and resistor would be shortedout but in the event the circuit was overloaded to the extent that thefuse or protector interrupted the circuit, a voltage would appear acrossthe lamp to visually indicate this condition. The use of series resistorand incandescent lamp has proved disadvantageous, particularly for lowvoltage circuits since, in one instance, when the fuse blows, currentwill flow through the lamp and also the small load devices which the lowvoltage circuit is operating, which may cause further breakdown in thecircuit or device. In another instance, in low voltage circuits, if aninstantaneous short circuit occurs and later corrects itself, sufiicientresistance remains in the load which, when added to the resistance inseries with the lamp, reduces the voltages across the lamp to a valueinsuificient to light the lamp. Also, in some equipment, particularly inaircraft, maintenance is performed with the power off. If a fuse hasblown during operation and the power shut off for maintenance no blownfuse indication is provided.

The principal object of the present invention is to ice provide aninexpensive and positive indicator arrangement for electrical circuits.

Another object is to provide an indicator arrangement which positivelyindicates that the fuse in a low voltage circuit has blown.

Still another object is to provide housing structure for assemblingelements of a circuit closer in a manner to be positively actuated bythe circuit current to indicate that the current is interrupted.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings, wherein:

FIG. 1 is a view in elevation of a load circuit with detailed structureof the elements of the invention sectioned to show their position whenthe load circuit is closed.

FIG. 2 is a view similar to FIG. 1 showing the position of the elementswhen the load circuit is open.

The circuit wires for a load (not shown) are indicated at 11 and 12 andwill receive power from a source. The circuit is provided with a fusereceptacle which may, as shown, take the form of spring clips 13 and 14which are supported by the terminal posts 15 and 16 of the respectivewires 11 and 12. A cylindrical fuse 17 is removably received between theclips 13 and 14 and forms part of the load circuit and, as is wellknown, the fuse blows or burns out when the circuit is overloaded andopens the circuit.

For the purpose of positively showing that the load circuit is open, anindicator circuit is connected in parallel with the fuse 17. Theindicator circuit is made up of a solenoid 20 having its coil connectedto the wires 11 and 12 respectively by leads 21 and 22 for actuating thecore 23, when the fuse 17 has blown, to control the position of anindicator pin 24.

As shown in the figures, a housing H is provided with a firstcompartment 25 for receiving the solenoid 20 and a second compartment 26is provided for receiving the pin 24. A passageway is located, as shown,in the housing structure providing communication between thecompartments and the solenoid 20 is positioned in compartment 25 so thatits core 23 is received in the passageway. The size of the passageway issuch that the core is snugly received therein but the core is movablefrom one to the other of its positions shown in FIG. 1 and FIG. 2. Thesecond compartment has an outer portion of relatively small or narrowcross section for receiving the pin 24 which has an abutment in the formof a flange 27 on its inner end. The flange 27 is received in the innerportion of the compartment 26 which is of relatively larger or widercross section than the outer portion and the inner and outer portions ofthe compartment have a common longitudinal axis and the core 23 isdisposed normal to this axis as shown in the drawings. The pin 24 isurged outwardly of the housing by means of a spring 28 which is locatedin the inner end of the compartment 26 and positioned in abuttingrelation with the inner face of the flange 27 as shown.

In FIG. 1, which is the position of the indicator elements when the loadcircuit is closed, the solenoid core 23 will be in its normal or outerposition and have its outer end in contact with the outer face of theflange 27 for maintaining the pin 24 in retracted position. The pin 24having been pushed inwardly to this position, against the pressure ofspring 28, when the fuse 17 was placed in the load circuit. When thefuse 17 has blown and the load circuit is opened, the solenoid 2%} isenergized by power through 214.2, contactor 29 and contacts 30 andfunctions to retract the core 23 to the position shown in FIG. 2releasing it from contact with the outer face of the flange 27 andpermitting the pin 24 to be sesame urged outwardly of the housing Hunder the force of the spring 28 as an indication that the fuse hasblown. The outer end of core 23 will then contact the side wall offlange 27 and maintain the solenoid contactor 29 separated from thecontacts 3ti39 until the blown fuse is replaced by a new fuse and thepin 24 is pushed inwardly to permit the core 23 to again move across theouter face of flange 27. The pin 24 may have its outer end suitablycolored to provide a ready visual indication to a maintenance operatorand tais is particularly desired when a number of circuits are providedwith the indicators as, for example, when a number of fuse receptaclesare supported on the inner face of a switchboard and the ends of theindicators are arranged to be visible from the outer face when a fusehas blown.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claim the invention maybe practiced otherwise than as specifically described.

What is claimed is:

Apparatus for visually indicating that an electrical load circuit isopen which comprises:

(a) an electromagnet formed of a coil and having a core movable from aforward position to a retracted position when the coil is energized,

(b) a parallel circuit between the coil and the load circuit having aswitch therein formed of a contactor fixed to said core and a pair or"contacts,

(0) said switch being closed when the core is in its forward position,

(d) a pin mounted for movement in a path normal to said core,

(c) said pin having a flange portion and an elongate portion extendingtherefrom,

(f) said flange portion having a side wall and an end wall generallynormal to each other,

(g) spring means positioning the flange side Wall to abut the end of thecore and prevent its movement to the forward position in order tomaintain the switch open,

(/1) said pin being movable against the spring means to adjust theposition of the flange and permit the core to ride over the end wall ofthe flange and advance to its forward position and close the switch and(1) means for holding the flange in this position until the coil becomesenergized by current passing through the parallel circuit and the coremoves to its retracted position whereby the pin is moved by the springmeans to a position indicating that the load circuit is open.

References Eited by the Examiner UNITED STATES PATENTS 143,679 10/72Doolittle.

623,444 4/ 99 Valentine.

646,721 4/00 Baker et a1. 1,418,748 6/22 Tregoe et al. 1,455,763 5/23Werner.

FOREIGN PATENTS 1,033,870 4/53 France.

E. JAMES SAX, Primary Examiner.

JOHN P. VVILDMAN, Examiner.

